This invention relates to a mass spectrometer including an ion source, a sector magnet, at least one detector, and both electric and magnetic quadrupole lenses.
In mass spectrometers the ion source generally produces a slightly divergent beam of ions having different masses but almost identical kinetic energy per ion charge by uniformly accelerating the ions in electric fields. The sector magnet produces a limited homogenous magnetic field which separates the ions according to their ratio of mass to charge (M/Q ratio) and focuses the ions of a certain M/Q ratio at one image point. The detector measures the intensity of the ion streams with a certain M/Q ratio at their focal or image points. In known single channel mass spectrometers, a single detector is used and the intensity of the magnetic field of the sector magnet is adjusted to the image point of a single stream of ions with a certain M/Q ratio. By changing the field intensity of the magnetic field of the sector magnet, the image points of the streams of ions with different M/Q ratios can be adjusted temporalily in succession on the detector and their intensity may be measured, but the ion streams which have not been so adjusted are lost for measurement purposes. To take a mass spectrum picture with such a prior art device is quite time consuming, and it can therefore only be used when the ion source operates constantly and the material source is sufficiently great. Quick phenomena which occur, for example, in a time period considerably less than a second, cannot be tracked or measured with such an instrument.
Since all ion streams with a certain M/Q ratio are focused simultaneously in the case of a constant magnetic field at corresponding spatially separate image points which together form a picture curve or plane, and the spreading of the image points of the various ion streams along the picture curve is called dispersion, multi-channel mass spectrometers are also known which have several detectors disposed on the picture curve. With such mass spectrometers it is possible to simultaneously measure the intensity of a number of ion streams with different M/Q ratios, corresponding to the number of detectors. It is also known to attach a detector at the place of the picture curve which is capable of simultaneously measuring all incident ion streams over a certain sector of the spectrum. For this purpose, photographic plates or channeltron honeycombs with suitable multi-channel detectors are used, and quick phenomena may also be recorded by such a photographic plate or the like. A mass spectrum cannot be directly registered in a computer memory, however, and a separate, second measuring process is required to evaluate the light absorption on the photographic plate, which is quite expensive. The photographic plate itself is also of significant size, which makes the mass spectrometer relatively bulky.
The deciding disadvantage of these known mass spectrometers is that the position of the picture curve and the dispersion are constant. Thus, fixedly adjusted detectors of a multi-channel spectrometer, for example, a mass spectrometer adjusted for a given isotrope frequency, may only be used for frequency measurements on a single element. Based on the invariable dispersion of known mass spectrometers, the isotope ions of another element with variable mass have other focal distances, so that the originally adjusted distances of the detectors must be mechanically realigned at considerable expense, if such alignment is possible. Moreover, only a certain range of the mass spectrum may be recorded by a multi-channel mass spectrometer, the terminal and starting masses of which range are at a certain fixed ratio. Larger or smaller parts of the spectrum cannot be recorded.